1. Field of the Invention
The present invention relates to an optical disk reproducing apparatus for reproducing information recorded on an optical disk, and more particularly to controlling of a spindle motor for rotating the optical disk.
2. Description of the Related Art
In an optical disk reproducing apparatus, a spindle motor for rotating an optical disk is controlled with a motor control signal generated on the basis of a synchronizing signal (frame sync) included in a reproducing signal output from an optical pickup in reproducing the optical disk. More particularly, the control for the spindle motor is made through a servo loop with PLL (Phase Locked Loop), and the motor control signal to the spindle motor is given by a voltage corresponding to a phase difference between the synchronizing signal and a preset reference signal, whereby the rotation of the spindle motor is controlled.
When reproducing information recorded on the optical disk, a predetermined voltage is firstly applied to the spindle motor and the optical disk begins to rotate by the rotation of the spindle motor. A phase comparison is made between the synchronizing signal included in the reproducing signal from the optical pickup and the preset reference signal, whereby the spindle motor is accelerated up to a predetermined range of rotational frequency. When the predetermined rotational frequency is reached, the servo loop with PLL is locked. When the servo loop with PLL cannot be locked due to some cause since the rotation of the spindle motor is accelerated, the rotational frequency of the spindle motor abnormally increases, resulting in a run-away phenomenon of the optical disk, which is turned in an uncontrolled state of the rotation.
For example, when the optical disk is reproduced by switching from one side to another, the rotation of the spindle motor is accelerated, until the optical pickup is moved to a reproducing position on the optical disk. Therefore, the rotational frequency of the spindle motor is increased, as the optical pickup reaches a positive position for a longer time, so that the optical disk is accelerated beyond a specified rotational frequency and the run-away phenomenon of the optical disk occurs.
Also, for example, when an outgoing beam from the optical pickup gets out of an effective recording area of the optical disk and enters a mirror face that has no tracks formed, the synchronizing signal cannot be detected so that the servo loop with PLL becomes disabled. As a result, the rotation of the spindle motor is accelerated to cause the optical disk to run away.
As conventional techniques for controlling the optical disk to be stopped when the run-away phenomenon of the optical disk occurs, there has been disclosed an optical disk player as disclosed in JP-A-7-032740, a DC motor control device as disclosed in JP-A-2000-125588, and a DC spindle motor speed detecting device as disclosed in JP-A-2001-078483. However, the conventional techniques includes following problems.
The optical disk player as disclosed in JP-A-7-032740 includes run-away sensing means for sensing a run-away of the spindle motor that drives the rotation of the optical disk, rotational direction sensing means for sensing the rotational direction of the spindle motor that runs away, and brake signal supplying means for supplying a brake signal having a polarity according to an output of the rotational direction sensing means to the spindle motor, whereby a run-away phenomenon of the optical disk is prevented by suppressing the spindle motor from running away.
However, the run-away sensing means senses a run-away of the spindle motor by detecting an electric current from the spindle motor, and the rotational direction sensing means senses the rotational direction of the spindle motor on the basis of an output voltage from the run-away sensing means. That is, the run-away sensing means employs the electric current for sensing, and the rotational direction sensing means employs a voltage for sensing. Therefore, the sensing operation is not necessarily stable, because that the electric current or voltage is likely to fluctuate depending on the operating condition.
The DC motor control device as disclosed in JP-A-2000-125588 includes intermittent braking voltage supplying means for intermittently supplying to a DC motor (corresponding to the spindle motor) a braking voltage having a polarity capable of electrically braking the DC motor, rotational direction determining means for determining the rotational direction of the DC motor by detecting the polarity of counter electromotive force of the DC motor during a period where no braking voltage is supplied to the DC motor, and control means for determining whether or not the rotational direction of the DC motor is reversed during a stop control period of the DC motor and stopping the supply of the intermittent braking voltage to the DC motor when the rotational direction is reversed, whereby a run-away phenomenon of the optical disk is prevented by suppressing the DC motor from running away.
However, the rotational direction determining means detects the polarity of counter electromotive force of the DC motor, but because the voltage of counter electromotive force is considerably low, and the voltage level of counter electromotive force is constant, it is difficult to stabilize the determining operation by the control means.
The DC spindle motor speed detecting device as disclosed in JP-A-2001-078483 includes a current/voltage converter for converting an electric current supplied to the spindle motor into a voltage, an analog/digital converter for converting an analog voltage converted by the current/voltage converter into a digital signal, and a control section for making the spindle motor control in accordance with the rotational speed of the spindle motor that is detected on the basis of the digital signal converted by the analog/digital converter, whereby a run-away phenomenon of the optical disk is prevented by suppressing the spindle motor from running away.
However, in technique described in JP-A-2001-078483, the rotational direction of the spindle motor is detected, employing a voltage based on a current applied to the spindle motor, but because the current is likely to fluctuate depending on the load condition, it is difficult to always stabilize the operation for detecting the rotational direction of the optical disk that runs away.
In addition to the conventional techniques as described above, there is a well known technique that when the optical disk runs away, a timer starts to measure time, and the operation is compulsorily turned in a stop mode after the elapse of a fixed time. However, the technique above has a problem that it takes a long-time to turn to the stop mode, and when the optical disk is reversely rotated and a brake signal in a direction of positive rotation is applied to the spindle motor, the optical disk is further accelerated in the opposite rotational direction, and not being stopped.